In subsea applications, the various casing strings are hung on a hanger in a concentric manner and in descending size order. The annular space between casing runs and the central production tubing is referred to as the A annulus. When production begins, thermal effects act on the fluid in the A annulus to raise its pressure. This occurs because by the nature of how subsea completions take place, the A annulus is full of seawater or/and well fluids, all of which are incompressible. When the production tubing heats up during production, the fluid in the A annulus is expanded. As a result, the casing has had to be sized to contain this pressure increase caused by warming an A annulus full of incompressible fluid. The need to contain the pressures encountered due to this heating effect causes additional expense for heavier walled casing and generally lengthens the time required to run the heavier casing into the well.
The present invention controls pressure buildup in the A annulus by replacing some of the incompressible fluid with compressible gas. It also provides filtration for the fluid displaced from the A annulus under the pressure of the compressible fluid which displaces it. These and other advantages of the present invention will be more apparent to those skilled in the arts from a review of the description of the preferred embodiment and the claims, which appear below.